We plan to isolate protein-DNA complexes from nuclei of D. melanogaster cells and embryos after treating the nuclei with agents, like SDS, which cause covalent attachment of nicking-closing enzymes to DNA; such treatments cause also covalent protein attachment to the DNA replication origin in SV40. The DNA protein complexes will be further cleaved with restriction enzymes and the protein bound DNA fragments will be characterized to determine if they represent a specific subset of the nuclear DNA restriction fragments. The protein bound DNA fragments belonging to specific genes (i.e. rDNA genes) will be mapped using the appropriate gene probes (i.e., Drosophila rDNA clones). In parallel experiments we shall cleave nuclear DNA under the mild conditions which preferentially digest non-nucleosomal DNA. By Southern hybridization with nick-translated DNA probes we shall determine whther specific DNA regions are hit, and we shall map these DNA regions vis a vis the protein-bound DNA fragments above. The specific non-nucleosomal DNA regions probably reflect a higher order DNA folding. We shall perform similar experiments in nuclei of pre- and postblastoderm embryos to determine whether (and how) such higher order structure of specific genes changes during development.